Search

The increasing CO 2 emissions from heavy industries have presented a growing threat to the global environment. The critical solution is to develop CO 2 sequestration technologies, especially the fast speed CO 2 fixation methods. In this study, the CO 2 uptake performances of hydrated cement paste under various environment parameters coupling with high temperature were evaluated through accelerated carbonation experiments. The results show that high temperature is an effective way to improve CO 2 sequestration efficiency, in which the waste heat accompanied by the emitted CO 2 can be used as the source of high temperature. Based on this, appropriate vapor and liquid water addition during carbonation can further improve the CO 2 sequestration performance of powder samples. Moreover, the hydration and carbonation products and the porosity before and after carbonation were evaluated, high temperature and vapor acceleration method facilitated aragonite generation and higher porosity reduction. Scale-up test of recycled aggregates on CO 2 sequestration under optimum carbonation conditions was evaluated, and the results show the CO 2 sequestration performance of recycled aggregates was stable in different input scales, which could sustain the CO 2 sequestration amount of 80kg/t-cem. [ABSTRACT FROM AUTHOR]

With the development of the circular economy and low-carbon society, the large-scale application of construction solid waste in buildings, such as recycled concrete, is becoming imperative. Accurately predicting the carbonation depth of recycled concrete is of great significance. Quantitatively analyzing the impact of each parameter on carbonation and elucidating the relationships between these parameters present challenges in predicting the carbonation of recycled concrete. In this study, different machine learning models and prediction equation models were applied and compared to predict the carbonation depth of 576 datasets associated with recycled concrete. The machine learning models used include Automation Machine Learning (AutoML), LightGBM, CatBoost, Neural Networks, Extra Trees, Random Forest, XGBoost, KNN (K-Nearest Neighbor). The results indicate that the machine learning method shows higher accuracy than the traditional equation, the AutoML model exhibits the best prediction accuracy among the investigated machine learning models, and carbonation test results further verified the favorable carbonation depth prediction effects of AutoML model. Furthermore, SHAP (Shapley Additive Explanations) was utilized to quantitatively analyze and explain the prediction results. The results demonstrate that carbonation time and the water to cement (W/C) ratio of recycled concrete have the most significant impact on the carbonation depth of recycled concrete buildings. • Different machine learning models and prediction equation models were applied and compared to predict the carbonation depth of 576 datasets associated with recycled concrete buildings. • AutoML model exhibits the best prediction accuracy among the investigated machine learning models, and carbonation test results further verified the favorable carbonation depth prediction effects of AutoML model. • The results demonstrate that carbonation time and the water to cement ratio of recycled concrete have the most significant impact on the carbonation depth of recycled concrete. [ABSTRACT FROM AUTHOR]

A comprehensive investigation was conducted to examine the influence of fly ash/slag mass ratio on the strength and microstructure of alkali-activated fly ash-slag (AAFS) mortars. NaOH and Na 2 SiO 3 were employed as activators for different fly ash/slag ratios. The results revealed that AAFS mortar with a fly ash/slag ratio of 25/75 exhibited the highest strength, reaching 104 MPa. The porosity and gel content of AAFS showed a weak correlation with compressive strength, emphasizing the significant impact of the generated gel type on AAFS strength. The comprehensive evaluation of AAFS strength incorporates factors related to the structure and chemical composition of reaction products. A strength index derived from AAFS mortar is proposed and validated against seven additional literature datasets from different systems, demonstrating a robust correlation between the calculated index and the compressive strength. Furthermore, carbon emission analysis reveals that, compared to OPC, FA100 exhibits 7.9%–21.2% lower carbon emissions, while FA25BF75 shows 0.1%–97.5% lower CO 2 intensity than OPC, owing to the higher strength of AAFS. In general, AAFS exhibits improved properties and environmental benefits, indicating significant potential for practical applications as a complete replacement for OPC. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing technology has received significant attention in construction building areas, and CO 2 curing has been proven to be an effective method to enhance the properties of cementitious materials and sequestrate CO 2. In this study, the mechanical properties of 3D printed mortar (3DPM) which had been subjected to CO 2 curing were investigated. The effects of curing time and the interlayer bonding types on the mechanical properties were discussed. The results show that appropriate CO 2 curing improved the mechanical properties of hardened 3DPM, especially the early age property, and the enhancement showed significant anisotropy in different test directions. In addition, the carbonation depths of the interlayers were higher than that of printed strips. Increasing carbonation time reduced the differences between the interlayer and strips' carbonation depths. Moreover, the carbonation extent of 3DPM was evaluated, and it was found that with an appropriate printing setting, the maximum carbonation ingression of 24% was attained in 24 h CO 2 curing. [ABSTRACT FROM AUTHOR]

• The application of carbonation of cement-based materials for carbon dioxide sequestration are summarized. • Revealing the carbonation acceleration mechanism and analyzing the influencing factors. • Research needs and application opportunities are discussed and recommended. In the past twenty years, significant researches have been conducted on the accelerating fixation technologies of carbon dioxide through the carbonation reaction of cement-based materials. In this study, the published literature on the application of carbonation of cement-based materials for carbon dioxide sequestration has been reviewed, the carbon dioxide sequestration capacity, the carbonation effect on the physical and mechanical behavior of recycled aggregates and concrete, the efficiency improvement methods, and the acceleration methods on the mechanical behavior of cement-based materials are discussed and summarized in detail. The comparative discussion results show that carbonation could effectively improve the mechanical performance of recycled aggregates and concrete. The parameters of liquid water content, sample size, environmental pressure, carbon dioxide concentration, and temperature significantly affect the sequestration efficiency of carbon dioxide of cement-based materials. Besides, the future application proposals of fast carbon dioxide sequestration technologies in the industrial areas and cement-based material recycling have been put forward. This review could facilitate the investigation and application of fast carbon dioxide sequestration technologies through the carbonation of cement-based materials. [ABSTRACT FROM AUTHOR]

• Proposed a rapid carbon dioxide sequestration method of through carbonation of cement-based materials at 300 °C–700 °C. • Smaller particle size around 100um could sequestrate 20 kg carbon dioxide per ton concrete in one minute. • A carbon dioxide sequestration procedure has been designed for future applications. In recent years, the increasing global temperature, caused by excessive carbon dioxide emission, has put a significant threat on the earth's environment. Therefore, the development of fast carbon dioxide sequestration technologies is urgently needed. In this study, a high-temperature carbonation technique has been proposed by using cement-based materials. The carbon dioxide sequestration efficiencies of cement paste were tested and evaluated from 300 °C to 700 °C, exhibiting different characteristics compared with that at ambient temperature, with optimum carbonation temperature at 600 °C. The operating parameters, such as carbonation time, sample size, vapor content, and water to cement ratio, which play a significant role in the carbonation reaction, have also been investigated and compared with that at ambient temperature. It was found that the high efficiency of carbon dioxide sequestration could be achieved in the samples with large size and low water to cement ratio. [ABSTRACT FROM AUTHOR]

• High temperature within limits accelerates the carbonation reaction speed. • Liquid water in the samples affects the high temperature carbonation reaction. • Environment vapor influences the carbonation of hydration products. The waste carbon dioxide generated in heavy industries usually accompanies by high temperatures and vapor. To fully utilize the high temperature and improve the carbon dioxide sequestration efficiency, this study has tested and evaluated the carbonation performance of cement paste in a broad temperature range from 20 °C to 300 °C. The results indicate that carbonation speed could be effectively improved under high temperatures in a short period (1 h) at the liquid water existing conditions. Besides, relative humidity and water to cement ratio effect at 100 °C were also investigated. The carbonation mechanisms at different vapor content have been explored from the viewpoint of carbonate substances transportation in high-temperature environments. The contribution of hydrated products to calcium carbonate varies with vapor content, and the high carbonation speed usually accompanies by the generation of the metastable calcium carbonate. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced plastics (GFRP) have been widely used in the field of civil engineering infrastructure, while it also generating a large amount of waste glass fibers simultaneously. This paper uses waste glass fiber in self compacting recycled concrete (SCRC), forming a kind of waste glass fiber reinforced self-compacting recycled concrete (RGF-SCRC). The effects of recycled coarse aggregate (RCA) replacement ratio, water to binder (W/B) ratio, the content and type of glass fiber on the working and mechanical properties of RGF-SCRC were investigated. The results showed that the specimens could meet the requirements of self-compacting concrete (SCC) in terms of working performance, but the addition of RCA and glass fiber could reduce the workability of RGF-SCRC, when RCA is replaced with 100 % and the fiber content reaches 10 kg/m3, the slump expansion is reduced by 9.5 % and 12.4 %, respectively. The mechanical properties of RGF-SCRC decreased as the growing value of RCA replacement ratio and the W/B ratio, among them, the elastic modulus decreased the most, by 40.4 % and 30.0 %, respectively. Compared with the results of the control specimen, the properties could be improved significantly under an appropriate content of waste glass fiber: the cube compressive strength, splitting tensile strength, flexural strength, and elastic modulus of RGF-SCRC were increased by 1.3∼9.6 %, 13.5∼59.4 %, 17.8∼40.9 %, and 3.3∼13.4 %, respectively. However, excessive fiber content showed a negative effect on the mechanical properties. Specimens with the 7.5 kg/m3 alkali resistant glass fiber content showed the best mechanical properties. Moreover, the X-ray CT and scanning electron microscope (SEM) techniques were applied to explore the influencing mechanism of waste glass fibers on RGF-SCRC. The results showed that after adding an appropriate content of waste glass fiber, the porosity and the number of large pores decreased, and the pore size and distribution became more reasonable, which enhanced the compactness of RGF-SCRC to some extent. The mechanical force and friction force anchored at the fiber end at the interface with the concrete matrix increase the bonding strength, thereby enhancing the mechanical properties of RGF-SCRC. This study achieve the resource utilization of waste glass fiber and improve the mechanical properties of concrete and the research results can provide a reference for the practical application of RGF-SCRC in civil engineering. • The waste glass fiber was applied in self compacting recycled concrete (SCRC). • Various parameters were investigated to make clear the influential mechanisms of glass fiber on the working and mechanical properties of waste glass fiber reinforced self-compacting recycled concrete. • The enhanced mechanism of fiber addition on SCRC was illustrated by the microstructure method and analysis. [ABSTRACT FROM AUTHOR]

The increasing global carbon dioxide concentration has received significant public attention in recent decades, with various sequestration methods being proposed by researchers all around the world. The enormous amount of generated cement-based building materials, such as waste concrete aggregate, particularly exhibits a great carbon dioxide fix potential through the carbonation process. However, the slow reaction speed in a normal environment prohibits its further application. On the other hand, exhaust carbon dioxide emitted from a cement factory is usually in a broad temperature range. Therefore, high temperature carbonation is proposed to accelerate the carbon dioxide sequestration speed in this study. The carbonation performance and carbon dioxide uptake rate of cement paste blocks and powder were evaluated in a broad temperature range (20 °C–300 °C), demonstrating that carbonation speed was greatly affected by temperature, with optimum carbonation temperature appearing at around 100 °C, at which cement paste samples could achieve the fastest carbonation speed at a rate of 16.4%/h in the first 1 h compare to 2.4%/h at normal temperature. In addition, the inner liquid water content of samples was another great influential factor which is related closely to the calcium carbonate generation rate from different hydrate substances, and adding liquid water into samples at appropriate time intervals could enhance carbonation reaction effectively, with the maximum improvement of 34.1%. Consequently, it was found that an improvement could be achieved at 100 °C in comparison with normal temperature, with a further increase of 721% being attained by adding liquid water every 20 min to 2 mm thickness cement paste blocks. [ABSTRACT FROM AUTHOR]

The outbreak of the COVID-19 epidemic has led to a large number of waste disposable medical face masks (DMFMs) worldwide, which seriously pollute the environment and threaten human health. In this paper, waste DMFMs were recycled as mask fiber and mixed into self-compacting recycled aggregates concrete (SCRAC) to form a mask fiber reinforced self-compacting recycled aggregates concrete (FRSCRAC). The effects of recycled coarse aggregate (RCA) replacement ratio, DMFM fiber content, and length on the working and mechanical properties of FRSCRAC were investigated. The results show that the specimens meet the requirements of self-compacting concrete (SCC) in terms of working and mechanical performance, but the RCA and DMFM fiber could reduce the workability of the FRSCRAC, and the higher the amount of RCA and DMFM fiber, the more obvious the reduction. At the same time, the mechanical properties of FRSCRAC increased as the decreasing RCA replacement ratio and growing DMFM fiber content. Compared with specimens without DMFM fiber reinforcement, the compressive strength, split tensile strength, flexural strength, and elastic modulus were increased by 1.3%-9.6%, 1.46%-8.6%, 24.4%-54.69%, and 0.65%-4.73%, respectively. Moreover, the reduction of the DMFM fiber length is favorable to the mechanical properties of FRSCRAC as well. Furthermore, the X-ray CT and scanning electron microscope (SEM-EDS) techniques were applied to analyze the microstructure of typical specimens. The results showed that the DMFM fiber and surrounding mortar could form a multiphase composite, which reduces the porosity and improves interfacial stress transfer efficiency, thus enhancing the mechanical properties of FRSCRAC. In addition, based on the experimental results, the mechanical strength index of FRSCRAC and the calculation formula of its mutual conversion relationship were proposed. The research conclusions of this paper can provide a reference for the application of waste DMFM fibers in FRSCRAC. • Waste disposable medical face masks were recycled as fiber and mixed into self-compacting recycled aggregate concrete. • Parameters were investigated to make clear the influential mechanisms of waste fiber on recycled concrete performance. • The mechanical strength index of FRSCRAC and the calculation formula of its mutual conversion relationship were proposed. [ABSTRACT FROM AUTHOR]

Fiber reinforced plastic (FRP) sandwich structure are increasingly used in construction areas recently for its high strength, light weight and corrosion resistance performance. This paper proposed an innovative composite sandwich structure incorporating GFRP skins, a cold formed profiled steel plate and a light weight balsa wood core. The interaction between the different components was connected by stainless steel core rivets. Three-point bending tests were conducted on eleven specimens to investigate the parameters (shear span to depth (a / d) ratio, thickness of cold formed profiled steel plate and spacing of the stainless steel core rivets) effect on the performance (deflection, ultimate load bearing capacity, and failure modes) of the new proposed structure. The test findings indicate that a reduction in ultimate load-bearing capacity ranging from 13% to 41%, accompanied by an escalation in deflection between 1.7 and 13.9 times, as the a / d ratio ranges from 1 to 6. All beams experienced failure at deflections ranging from span/114 to span/50. Specifically, specimens displayed core shear failure for a / d ratios ≤ 4, transitioning to top skin compression failure at an a / d ratio of 6. Compared to specimens without cold formed profiled steel plate reinforcement, the load bearing capacity of the new proposed composite structure at serviceability limit states and ultimate limit states was increased by 68%−194% and 53%−83%, respectively. Moreover, the reinforcement of the stainless steel core rivets can ensure the coordinated working of different components, and the smaller the spacing, the better the working effect. Finally, an analytical model was developed to account for the impact of cold-formed profiled steel plates on specimen stiffness and load-bearing capacity. This model was subsequently validated through experimental results. Both the experimental and theoretical analysis verified the favorable performance of the proposed new composite structure. • A novel composite sandwich structure was proposed. • The shear span to depth ratio plays a significant role in the ultimate and service limit, and load bearing capacity of the new proposed structure. • The new proposed structure shows significant advantages in load bearing capacity. • The proposed predicted formula verified by test results considering the combined effect of cold formed profiled steel plate shows favorable prediction accuracy. [ABSTRACT FROM AUTHOR]

This paper presents a systematic experimental study on the fracture behavior of low-carbon mortars with various contents of carbonated recycled sand and recycled powder (CRS and CRP). Three-point bending tests on pre-notched beams were performed to explore the load-induced fracture processes. Based on the strain and displacement fields measured using the digital image correlation technique, the evolution of the fracture process zone (FPZ) was studied qualitatively and quantitatively. Results indicated that the initial cracking toughness (K Ic ini), unstable fracture toughness (K Ic un) and fracture energy (G f) of mortar reduced gradually with the increasing recycled sand (RS) content but kept relatively steady with the rising recycled powder (RP) dosage except for K Ic ini. Carbonation treatment could effectively improve the K Ic ini of mortar with low RP content and G f with a high proportion of RS but had limited effect on K Ic un. A combination of the FPZ evolution characteristics and crack growth resistance curves suggested that the use of RS would increase microcracking in the stable crack growth stage and thus facilitate the connectivity of microcracks in the unstable fracture stage, while the use of RP mainly affected the crack initiation stage of cement paste in the mortar. The improvement of mortar fracture by CO 2 treatment of RS or RP also corresponded to these stages. Regarding fracture characteristics and carbon footprint, mortars with CRS and CRP could achieve a synergy of safety and low carbon and thus can be considered as low-carbon cementitious materials compared to normal mortar. [ABSTRACT FROM AUTHOR]

Recycling of construction and demolition wastes (CDW) for the development of intelligent construction materials has the potential to lower the environmental burden and promote the development of intelligent construction. Herein, CO 2 pretreatment to a type of recycled fine aggregate (RFA) was employed to upcycle the waste for developing 3D printable mortar (3DPM). The replacement ratios of natural fine aggregates (NFA) by recycled fine aggregates (RFA) and carbonated recycled fine aggregates (CRFA) up to 100% were designed, and the engineering properties, including compressive strength, flexural strength and interlayer bonding strength, of 3DPM were investigated. Comprehensive microscopic tests with X-ray diffraction (XRD), scanning electron microscopy-backscattered electrons (SEM-BSE), and X-ray computed tomography (X-CT), were used to demonstrate the microstructure mechanism of the 3DPM specimens with upcycled fine aggregates at the microscopic level. Systematical enhancements in engineering properties of 3DPM with CRFA were reported when compared with those of 3DPM with RFA. The compressive strength at 28 days was noticeably enhanced by 68.5% for the 3DPM with 100% upcycled fine aggregates. Carbonation enables significant calcite precipitates in the adhered cement paste area and formation of cement hydrates in the new cement paste area. The findings of the present work not only deepen the understandings in the microstructure alterations of RFA by CO 2 pretreatments, but also pave a path towards the upcycling of CDW towards sustainable intelligent constructions. [ABSTRACT FROM AUTHOR]

In recent years, particle damper has been proved to be an effective vibration control strategy in various fields. In this study, an energy-evaluation model of particle tuned mass damper (PTMD) attached on a Multi Degree of Freedom (MDOF) structure (76-story high-rise building) under wind excitation is established based on an equivalent simplified method, and the simulation results are validated by a wind tunnel experiment. The energy related in the whole structural system, including the kinetic energy, elastic potential energy, energy dissipated by the structural damping and external input energy, has been analyzed in detail, and the energy transmission effect between the main structure and the attached PTMD has been investigated through the time history response of the input energy distribution. It is found that PTMD shows favorable energy dissipation performance, a large percentage of the input energy transfers from the main structure to PTMD in the first few seconds, and after that the particle-container wall collision consumes the main proportion of the input energy. Moreover, a series of systematic parametric analyses are conducted, including volume filling ratio, PTMD auxiliary mass ratio, particle damping coefficient and frequency ratio of PTMD. Furthermore, a full factorial study is conducted to investigate the interaction effect of different parameters. The results show that the combination of the parameters has a significant effect on the energy dissipation performance of PTMD, a parametric designing procedure has been given accordingly. • An energy-evaluation model of PTMD attached on a MDOF structure is proposed and verified by a wind tunnel experiment. • The energy distribution and transmission between the main structure and PTMD is analyzed by the time history response. • Parametric analyses of PTMD are conducted and a parametric designing procedure is suggested accordingly. [ABSTRACT FROM AUTHOR]

Accelerated carbonation of recycled aggregates (RAs) enables fast carbon sequestration while improving engineering properties of prepared concrete. This paper presents a systematic experimental study on the fracture behaviour of concrete with carbonated recycled coarse and fine aggregates (RCA and RFA), in terms of fracture parameters and fracture process zone (FPZ). The relevant influencing mechanism was investigated by relating the macroscopic fracture responses to microstructural features. Results indicate that carbonated RFA mainly enhanced the initial fracture toughness of concrete, while carbonated RCA primarily increased its unstable fracture toughness. The enhancement of fracture energy was closely associated with carbonated RCA and RFA. The utilization of RFA resulted in the looseness and higher porosity of mortar matrix, which reduced the crack initiation resistance of concrete, mainly affecting its initial cracking stage. The incorporation of RCA reduced crack bifurcation and deflection of concrete, leading to a smaller width of FPZ, which made the initial descending segment of the tension softening curve (TSC) steeper and its tail segment shorter. The carbonation treatment of RAs improved the densification of the adhered old mortar and reduced the porosity of prepared concrete, rising the cracking resistance and inducing a wider FPZ. As a result, the initial descending segment of TSC became flatter and its tail segment tended to be longer. • Roles of carbonated recycled fine and coarse aggregates in concrete fracture are explored. • Fracture process zone is systematically characterized based on DIC and inverse analysis. • Fracture mechanism is discussed from both microscopic and macroscopic viewpoints. • Recycled fine and coarse aggregates respectively affect the crack initiation and propagation. [ABSTRACT FROM AUTHOR]

In this study, natural aggregates, recycled aggregates (RAs), and carbonated RAs were combined to prepare concrete. Strength, drying shrinkage, microstructures, and the carbon emissions of concrete prepared with different aggregate combinations were explored and compared. The results show that the compressive strengths of carbonated fully recycled aggregate concrete (CFRAC) increased by 20.9% and the drying shrinkage at 180 days decreased by 23.3% compared with that of concrete with RAs due to the reduction of water absorption of RAs and the additional water. The pore structure of CFRAC was densified and improved by carbonation treatment on RAs. Furthermore, the carbon emission analysis showed that CFRAC had 7.1%∼13.3% lower carbon emission and 13.4%∼18.4% lower CO 2 intensity than natural/recycled aggregate concrete due to the shorter transportation distance and the carbon absorption. Generally, CFRAC had improved properties and environmental benefits, which shows carbonation treatment is a valuable way to promote waste concrete recycling. [Display omitted] • Carbonated recycled aggregates (CRAs) improve concrete strength and reduce variability. • CO 2 treatment for recycled fine/coarse aggregates reduces the shrinkage of concrete. • CRA concrete has environmental benefits due to low CO 2 emission and high strength. [ABSTRACT FROM AUTHOR]

• The increased carbonation temperature (70℃) accelerate the carbonation speed of recycled aggregates; • The modified aggregates through accelerated carbonation show better physical properties relative to normal recycled aggregates; • The mechanical performances of recycled concrete prepared with the modified aggregates were also improved. Carbonation can modify waste concrete aggregate and sequester CO 2 ; however, the slow reaction speed in a room environment limits its industrial application. In this study, the carbonation reaction of recycled coarse aggregates were accelerated at 70 °C. The physical properties of the recycled coarse aggregate before and after accelerated carbonation treatment and the mechanical properties of recycled concrete were tested and evaluated. Based on the results, an increased carbonation temperature can accelerate the carbonation reaction rate of the recycled concrete aggregate. The calcium hydroxide contained was fully carbonated in the first 12 h. Carbonation modification reduced the water absorption rate to 23.6% and the crushing value to 36.2%. Moreover, the mechanical performance of recycled concrete mixed with carbonation-modified aggregates was evaluated through a uniaxial stress–strain constitutive test. The 28 d compressive strength showed a 14.2% increase at 100% substitution of recycled modified aggregates relative to recycled aggregates. The elastic modulus and brittleness of the recycled concrete were also improved. [ABSTRACT FROM AUTHOR]